U.S. patent number 10,287,646 [Application Number 14/899,275] was granted by the patent office on 2019-05-14 for porous metal body and method for producing same.
This patent grant is currently assigned to SUMITOMO ELECTRIC INDUSTRIES, LTD., SUMITOMO ELECTRIC TOYAMA CO., LTD.. The grantee listed for this patent is SUMITOMO ELECTRIC INDUSTRIES, LTD., SUMITOMO ELECTRIC TOYAMA CO., LTD.. Invention is credited to Masatoshi Majima, Kazuki Okuno, Hidetoshi Saito, Hitoshi Tsuchida, Kengo Tsukamoto.
United States Patent |
10,287,646 |
Okuno , et al. |
May 14, 2019 |
Porous metal body and method for producing same
Abstract
Provided is a porous metal body having superior corrosion
resistance to conventional metal porous bodies composed of
nickel-tin binary alloys and conventional metal porous bodies
composed of nickel-chromium binary alloys. The porous metal body
has a three-dimensional network skeleton and contains at least
nickel, tin, and chromium. The concentration of chromium contained
in the porous metal body is highest at the surface of the skeleton
of the porous metal body and decreases toward the inner side of the
skeleton. In one embodiment, the chromium concentration at the
surface of the skeleton of the porous metal body is more preferably
3% by mass or more and 70% by mass or less.
Inventors: |
Okuno; Kazuki (Itami,
JP), Majima; Masatoshi (Itami, JP),
Tsukamoto; Kengo (Imizu, JP), Tsuchida; Hitoshi
(Imizu, JP), Saito; Hidetoshi (Imizu, JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
SUMITOMO ELECTRIC INDUSTRIES, LTD.
SUMITOMO ELECTRIC TOYAMA CO., LTD. |
Osaka-shi, Osaka
Imizu-shi, Toyama |
N/A
N/A |
JP
JP |
|
|
Assignee: |
SUMITOMO ELECTRIC INDUSTRIES,
LTD. (Osaka-shi, Osaka, JP)
SUMITOMO ELECTRIC TOYAMA CO., LTD. (Imizu-shi, Toyama,
JP)
|
Family
ID: |
52104338 |
Appl.
No.: |
14/899,275 |
Filed: |
April 9, 2014 |
PCT
Filed: |
April 09, 2014 |
PCT No.: |
PCT/JP2014/060253 |
371(c)(1),(2),(4) Date: |
December 17, 2015 |
PCT
Pub. No.: |
WO2014/203594 |
PCT
Pub. Date: |
December 24, 2014 |
Prior Publication Data
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|
|
Document
Identifier |
Publication Date |
|
US 20160130678 A1 |
May 12, 2016 |
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Foreign Application Priority Data
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|
|
|
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Jun 19, 2013 [JP] |
|
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2013-128785 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
C22C
1/0433 (20130101); H01M 4/80 (20130101); H01M
8/0232 (20130101); C21D 9/0068 (20130101); C25D
7/00 (20130101); C23C 14/34 (20130101); C23C
28/021 (20130101); C22F 1/11 (20130101); C23C
14/5873 (20130101); C25D 15/00 (20130101); C23C
28/028 (20130101); C25D 5/505 (20130101); B22F
7/002 (20130101); C22C 1/08 (20130101); C22F
1/02 (20130101); C22F 1/10 (20130101); C23C
28/027 (20130101); C25D 5/12 (20130101); C25D
5/14 (20130101); C22F 1/16 (20130101); C25D
5/50 (20130101); C23C 14/14 (20130101); C25D
3/04 (20130101); C25D 1/08 (20130101); C25D
5/56 (20130101); C25D 3/06 (20130101); B22F
2999/00 (20130101); C25D 3/12 (20130101); B22F
2207/01 (20130101); Y02E 60/50 (20130101); Y02E
60/10 (20130101); C25D 3/30 (20130101); Y02T
50/60 (20130101); B22F 2999/00 (20130101); B22F
7/002 (20130101); B22F 2003/248 (20130101) |
Current International
Class: |
C21D
9/00 (20060101); H01M 8/0232 (20160101); C23C
28/02 (20060101); C25D 3/04 (20060101); C23C
14/58 (20060101); C23C 14/34 (20060101); C23C
14/14 (20060101); C22F 1/16 (20060101); C22F
1/02 (20060101); C22F 1/10 (20060101); C22F
1/11 (20060101); C22C 1/04 (20060101); B22F
7/00 (20060101); C25D 15/00 (20060101); C25D
5/56 (20060101); C25D 5/50 (20060101); C25D
5/14 (20060101); H01M 4/80 (20060101); C22C
1/08 (20060101); C25D 7/00 (20060101); C25D
5/12 (20060101); C25D 1/08 (20060101); C25D
3/12 (20060101); C25D 3/30 (20060101); C25D
3/06 (20060101) |
Field of
Search: |
;148/427 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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|
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|
|
1177846 |
|
Apr 1998 |
|
CN |
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55-018579 |
|
Feb 1980 |
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JP |
|
H4-83713 |
|
Mar 1992 |
|
JP |
|
H11-154517 |
|
Jun 1999 |
|
JP |
|
2005-280164 |
|
Oct 2005 |
|
JP |
|
4378202 |
|
Dec 2009 |
|
JP |
|
2012-132083 |
|
Jul 2012 |
|
JP |
|
2012-149282 |
|
Aug 2012 |
|
JP |
|
WO-2013/099532 |
|
Jul 2013 |
|
WO |
|
WO-2014/050536 |
|
Apr 2014 |
|
WO |
|
Primary Examiner: Zhu; Weiping
Attorney, Agent or Firm: Drinker Biddle & Reath LLP
Claims
The invention claimed is:
1. A porous metal body having a skeleton with a three-dimensional
network structure and comprising at least nickel, tin, and
chromium, wherein a concentration of chromium contained in the
porous metal body is highest at a surface of the skeleton of the
porous metal body and decreases toward an inner side of the
skeleton, the concentration of chromium at the surface of the
skeleton is 4 to 30 times higher than an average chromium
concentration of the skeleton.
2. The porous metal body according to claim 1, wherein the
concentration of chromium at the surface of the skeleton of the
porous metal body is 3% by mass or more and 70% by mass or
less.
3. A method for producing the porous metal body according to claim
1, the method comprising: a conductive coating layer forming step
of forming a conductive coating layer on a surface of a porous base
composed of a resin material; a nickel layer forming step of
forming a nickel layer on a surface of the conductive coating
layer; a chromium-dispersed tin layer forming step of forming a tin
layer on a surface of the nickel layer, the tin layer containing
dispersed chromium particles; and a heat treatment step of inducing
interdiffusion of metal atoms between the nickel layer and the tin
layer containing dispersed chromium particles.
4. The method for producing the porous metal body according to
claim 3, wherein the chromium-dispersed tin layer forming step
includes a chromium-particle-dispersing step of supplying chromium
particles to a tin plating bath and stirring the tin plating bath
to disperse the chromium particles in the tin plating bath; and a
chromium-dispersed tin plating step of immersing the nickel layer
in the tin plating bath.
5. A method for producing the porous metal body according to claim
1, the method comprising: a conductive coating layer forming step
of forming a conductive coating layer on a surface of a porous base
composed of a resin material; a nickel layer forming step of
forming a nickel layer on a surface of the conductive coating
layer; a tin layer forming step of forming a tin layer on a surface
of the nickel layer; a chromium layer forming step of forming a
chromium layer on a surface of the tin layer; and a heat treatment
step of inducing interdiffusion of metal atoms between the nickel
layer, the tin layer, and the chromium layer.
6. The method for producing the porous metal body according to
claim 5, wherein, in the chromium layer forming step, the chromium
layer is formed on the surface of the tin layer by a gas phase
method.
7. The method for producing the porous metal body according to
claim 5, wherein, in the chromium layer forming step, the chromium
layer is formed on the surface of the tin layer by immersing the
tin layer in a chromium plating bath.
8. The method for producing the porous metal body according to
claim 5, wherein, in the chromium layer forming step, the chromium
layer is formed on the surface of the tin layer by applying a
mixture of chromium particles and a binder to the surface of the
tin layer.
9. A method for producing the porous metal body according to claim
1, the method comprising: a conductive coating layer forming step
of forming a conductive coating layer on a surface of a porous base
composed of a resin material; a nickel-tin alloy layer forming step
of forming a nickel-tin alloy layer on a surface of the conductive
coating layer; a chromium layer forming step of forming a chromium
layer on a surface of the nickel-tin alloy layer; and a heat
treatment step of inducing interdiffusion of metal atoms between
the nickel-tin alloy layer and the chromium layer.
10. The method for producing the porous metal body according to
claim 9, wherein, in the chromium layer forming step, the chromium
layer is formed on the surface of the nickel-tin alloy layer by a
gas phase method.
11. The method for producing the porous metal body according to
claim 9, wherein, in the chromium layer forming step, the chromium
layer is formed on the surface of the nickel-tin alloy layer by
immersing the nickel-tin alloy layer in a chromium plating
bath.
12. The method for producing the porous metal body according to
claim 9, wherein, in the chromium layer forming step, the chromium
layer is formed on the surface of the nickel-tin alloy layer by
applying a mixture of chromium particles and a binder to the
surface of the nickel-tin alloy layer.
Description
TECHNICAL FIELD
The present invention relates to a porous metal body that can be
used in current collectors of various batteries, capacitors, fuel
cells, etc.
BACKGROUND ART
A method for producing a porous metal body, including performing an
electrical conduction treatment on a resin porous body, forming an
electroplating layer composed of metal on the treated resin porous
body, and, if needed, burning away the resin porous body is known.
An example thereof is described in PTL 1.
A porous metal body composed of a nickel-tin alloy has been
proposed as a porous metal body that has oxidation resistance,
corrosion resistance, and high porosity and is suitable for use in
current collectors of various batteries, capacitors, fuel cells,
etc. An example thereof is described in PTL 2.
A porous metal body composed of a nickel-chromium alloy has been
proposed as a porous metal body having high corrosion resistance.
An example thereof is described in PTL 3.
CITATION LIST
Patent Literature
[PTL 1] Japanese Unexamined Patent Application Publication No.
11-154517
[PTL 2] Japanese Unexamined Patent Application Publication No.
2012-132083
[PTL 3] Japanese Unexamined Patent Application Publication No.
2012-149282
SUMMARY OF INVENTION
Technical Problem
However, in recent years, there has been increasing demand for
batteries, capacitors, fuel cells, etc., with higher output and
higher capacity (size reduction), and under such circumstances,
metal porous bodies that constitute current collectors are required
to achieve further improvements in their oxidation resistance and
corrosion resistance.
An object of the present invention is to provide a porous metal
body that has superior corrosion resistance to conventional metal
porous bodies composed of nickel-tin binary alloys and metal porous
bodies composed of nickel-chromium binary alloys.
Solution to Problem
The inventors of the present invention have found that the
above-described object can be achieved by a porous metal body that
has a three-dimensional network skeleton and contains at least
nickel, tin, and chromium, in which the concentration of chromium
contained in the porous metal body is highest at a surface of the
skeleton of the porous metal body and decreases toward the inner
side of the skeleton.
The structure described above permits intentional or unintentional
inclusion of at least one element other than nickel, tin, and
chromium in the porous metal body provided that the object
described above can be achieved.
Advantageous Effects of Invention
According to the present invention, a porous metal body that has
superior corrosion resistance to conventional metal porous bodies
composed of nickel-tin binary alloys and conventional metal porous
bodies composed of nickel-chromium binary alloys can be
provided.
DESCRIPTION OF EMBODIMENTS
In the description below, aspects of the present invention are
described.
(1) A porous metal body according to an aspect of the present
invention has a three-dimensional network skeleton and contains at
least nickel, tin, and chromium, in which the concentration of
chromium contained in the porous metal body is highest at the
surface of the skeleton of the porous metal body and decreases
toward the inner side of the skeleton.
According to the aspect (1) described above, a porous metal body
having superior corrosion resistance to conventional metal porous
bodies composed of nickel-tin binary alloys and conventional metal
porous bodies composed of nickel-chromium binary alloys can be
provided.
In particular, according to the aspect (1) described above, it is
possible to increase the chromium concentration at the surface of
the skeleton of the porous metal body, the surface being the place
having the largest influence on corrosion resistance of the porous
metal body, by using less chromium (on a mass basis) compared to a
porous metal body having a completely homogeneous chromium
concentration.
Thus, compared to a porous metal body having a homogeneous chromium
concentration from the surface to the inner side of the skeleton,
the amount of chromium used in production and the cost for raw
materials can be suppressed.
Moreover, a significantly high temperature (for example,
1200.degree. C.) must be held for a long time in order to evenly
diffuse chromium throughout the skeleton of the porous metal body,
and thus the energy cost is high.
In contrast, the aspect (1) only requires a minimum required amount
of chromium be diffused from the surface of the skeleton of the
porous metal body, and thus it is possible to improve corrosion
resistance of a porous metal body while saving the energy cost
required to diffuse chromium.
In addition to the aspect (1) above, the following aspect (2) is
preferably employed.
(2) The chromium concentration at the surface of the skeleton of
the porous metal body is preferably 3% by mass or more and 70% by
mass or less and more preferably 5% by mass or more and 50% by mass
or less.
According to the aspect (2), high corrosion resistance and high
mechanical strength can be obtained and, at the same time,
electrical conductivity suitable for current collectors can be
obtained.
When the chromium concentration at the surface of the skeleton of
the porous metal body is less than 3% by mass, corrosion resistance
is degraded.
When the chromium concentration at the surface of the skeleton of
the porous metal body is more than 70% by mass, contact resistance
is increased due to a large fraction of chromium oxides at the
surface of the skeleton.
The inventors of the present invention have found that the porous
metal body that achieves the object described above can be produced
according to aspects (3) to (12) described below.
(3) A method for producing the porous metal body described in (1)
or (2) above includes a conductive coating layer forming step of
forming a conductive coating layer on a surface of a porous base
composed of a resin material; a nickel layer forming step of
forming a nickel layer on a surface of the conductive coating
layer; a chromium-dispersed-tin layer forming step of forming a tin
layer on a surface of the nickel layer, the tin layer containing
dispersed chromium particles; and a heat treatment step of inducing
interdiffusion of metal atoms between the nickel layer and the tin
layer containing dispersed chromium particles under heating.
According to the aspect (3), a tin layer having a high chromium
content can be formed on a surface of the porous skeleton.
Preferably, the aspect (4) below is employed in addition to the
aspect (3) above.
(4) The chromium-dispersed-tin layer forming step includes a
chromium-particle-dispersing step of supplying chromium particles
to a tin plating bath and stirring the tin plating bath so as to
disperse chromium particles in the tin plating bath; and a
chromium-dispersed-tin plating step of immersing the nickel layer
in the tin plating bath.
According to the aspect (4), chromium particles can be evenly
dispersed in the surface of the skeleton of the porous body.
(5) A method for producing the porous metal body described in (1)
or (2) above includes a conductive coating layer forming step of
forming a conductive coating layer on a surface of a porous base
composed of a resin material; a nickel layer forming step of
forming a nickel layer on a surface of the conductive coating
layer; a tin layer forming step of forming a tin layer on a surface
of the nickel layer; a chromium layer forming step of forming a
chromium layer on a surface of the tin layer; and a heat treatment
step of inducing interdiffusion of metal atoms between the nickel
layer, the tin layer, and the chromium layer.
According to the aspect (5), the chromium concentration at the
surface of the skeleton of the porous body can be increased.
Preferably, the aspect (6) below is employed in addition to the
aspect (5) above.
(6) In the chromium layer forming step, the chromium layer is
formed on the surface of the tin layer by a gas phase method.
According to the aspect (6), a layer having a high chromium
concentration can be formed on the surface of the skeleton of the
porous body by using less chromium.
Preferably, the aspect (7) below is employed in addition to the
aspect (5) above.
(7) In the chromium layer forming step, the chromium layer is
formed on the surface of the tin layer by immersing the tin layer
in a chromium plating bath.
According to the aspect (7), a layer having a high chromium
concentration can be formed on the surface of the skeleton of the
porous body by using less chromium.
Preferably, the aspect (8) below is employed in addition to the
aspect (5) above.
(8) In the chromium layer forming step, the chromium layer is
formed on the surface of the tin layer by applying a mixture of
chromium particles and a binder to the surface of the tin
layer.
According to the aspect (8), a layer having a high chromium
concentration can be formed on the surface of the skeleton of the
porous body.
(9) A method for producing the porous metal body described in (1)
or (2) above includes a conductive coating layer forming step of
forming a conductive coating layer on a surface of a porous base
composed of a resin material; a nickel-tin alloy layer forming step
of forming a nickel-tin alloy layer on a surface of the conductive
coating layer; a chromium layer forming step of forming a chromium
layer on a surface of the nickel-tin alloy layer; and a heat
treatment step of inducing interdiffusion of metal atoms between
the nickel-tin alloy layer and the chromium layer.
According to the aspect (9), since nickel and tin are alloyed in
advance, the heat treatment time for diffusing these elements can
be shortened.
Preferably, the aspect (10) below is employed in addition to the
aspect (9) above.
(10) In the chromium layer forming step, the chromium layer is
formed on the surface of the nickel-tin alloy layer by a gas phase
method.
According to the aspect (10), a layer having a high chromium
concentration can be formed on the surface of the skeleton of the
porous body by using less chromium.
Preferably, the aspect (11) below is employed in addition to the
aspect (9) above.
(11) In the chromium layer forming step, the chromium layer is
formed on the surface of the nickel-tin alloy layer by immersing
the nickel-tin alloy layer in a chromium plating bath.
According to the aspect (11), a layer having a high chromium
concentration can be formed on the surface of the skeleton of the
porous body by using a small amount of chromium.
Preferably, the aspect (12) below is employed in addition to the
aspect (9) above.
(12) In the chromium layer forming step, the chromium layer is
formed on the surface of the nickel-tin alloy layer by applying a
mixture of chromium particles and a binder to the surface of the
nickel-tin alloy layer.
According to the aspect (12), a layer having a high chromium
concentration can be formed on the surface of the skeleton of the
porous body.
A specific example of the "porous metal body having a
three-dimensional network skeleton" is Celmet (registered trademark
of Sumitomo Electric Industries, Ltd.).
The "porous base composed of a resin material" may be any known or
commercially available porous material composed of a resin.
Specific examples of the porous base composed of a resin material
include any one or combination of a foam body composed of a resin
material, a nonwoven cloth composed of a resin material, a felt
composed of a resin material, and a three-dimensional network
object composed of a resin material.
The resin material constituting the porous base may be of any type
but is preferably a material that can be burned away. Specific
examples of the foam body composed of a resin material include
urethane foam, styrene foam, and melamine foam resin. Urethane foam
and the like are preferable from the viewpoint of increasing the
porosity of the porous base. When the porous base has a sheet
shape, the porous base is preferably composed of a flexible (does
not break when bent) material from the handling viewpoint.
The porosity of the porous base is not limited and is appropriately
selected according to the usage. The porosity is typically 60% or
more and 98% or less and more preferably 80% or more and 96% or
less.
The thickness of the porous base is not limited and is
appropriately selected according to the usage. The thickness is
typically 150 .mu.m or more and 5000 .mu.m or less, more preferably
200 .mu.m or more and 2000 .mu.m or less, and yet more preferably
300 .mu.m or more and 1200 .mu.m or less.
The "conductive coating layer" refers to an electrically conductive
layer formed on the surface of the porous base composed of a resin
material.
Any methods capable of forming a conductive coating layer on the
surface of the porous base can be employed in the "conductive
coating layer forming step". Specific examples of the "conductive
coating layer forming step" includes a method of applying a mixture
of electrically conductive particles (for example, particles of
metal materials such as stainless steel and particles of carbon
such as crystalline graphite, amorphous carbon black, etc.) and a
binder to the surface of the porous base and a method of forming a
layer composed of an electrically conductive metal material on the
surface of the porous base by electroless plating, sputtering,
vapor-deposition, ion-plating, or the like.
Specific examples of the electroless plating using nickel include a
method of immersing the porous base in a known electroless nickel
plating bath such as an aqueous nickel sulfate solution containing
sodium hypophosphite or the like. If needed, the porous base may be
immersed in an activating solution (washing solution produced by
Japan Kanigen Co., Ltd.) containing a small amount of palladium
ions prior to immersing the porous base in the plating bath.
Specific examples of sputtering using nickel include a method that
involves fixing the porous base onto a substrate holder and
applying DC voltage between the substrate holder and a target
(nickel) while introducing inert gas so as to cause ionized inert
gas to collide with nickel and inducing flying nickel particles to
deposit onto the surface of the porous base, etc.
The conductive coating layer is to be continuously (in a manner
that allows conduction) formed on the surface of the porous base
and the metal plating weight thereof (amount attached to the porous
base) is not limited. For example, when nickel is used to form the
conductive coating layer, the coating weight is typically 5
g/m.sup.2 or more and 15 g/m.sup.2 or less and more preferably 7
g/m.sup.2 or more and 10 g/m.sup.2 or less.
The "nickel layer" is a layer composed of nickel (elemental
nickel). Intentional or unintentional incorporation of at least one
element other than nickel is permissible as long as the object
described above is achievable.
Specific examples of "chromium particles" include particles of
elemental chromium and particles of chromium oxides.
The "the tin layer containing dispersed chromium particles" is a
layer composed of tin (elemental tin) with chromium particles
dispersed therein. Intentional or unintentional incorporation of at
least one element other than tin in the portion formed of tin
(elemental tin) is permissible as long as the object described
above is achievable.
The "tin layer" is a layer composed of tin (elemental tin).
Intentional or unintentional incorporation of at least one element
other than tin is permissible as long as the object described above
is achievable.
The "chromium layer" is a layer composed of chromium (elemental
chromium) or chromium oxide. Intentional or unintentional
incorporation of at least one element other than chromium is
permissible as long as the object described above is
achievable.
The "gas phase method" is a generic name of techniques for forming
thin films by using gas. Specific examples of the gas phase method
include sputtering, a vapor deposition method, ion plating, and
pulsed laser deposition (PLD).
The "binder" is a material that fixes chromium particles onto the
surface of the skeleton of the porous body. Specific examples of
the binder include various known materials such as polyvinylidene
fluoride, styrene butadiene rubber, carboxymethyl cellulose,
polytetrafluoroethylene, polyethylene, polypropylene, and polyvinyl
alcohol.
The porous base composed of a resin material can be removed by
burning or dissolving in a chemical solution.
In the case where the porous base composed of a resin material is
to be removed by burning and the difference between the temperature
of burning the porous base composed of a resin material and the
temperature at which the porous metal body is held during the heat
treatment step is small, the heat treatment step may also serve as
the step of removing the porous base composed of a resin material
(the porous base composed of a resin material can be removed in the
heat treatment step).
EXAMPLES
(Example 1) Chromium-Particle-Dispersed Plating
Details of Example 1 are described below. Example 1 provides a
nickel-tin-chromium porous alloy body and is an embodiment of the
present invention.
(Electrical Conduction Treatment on Three-Dimensional Network
Resin)
First, a polyurethane foam sheet (cell size: 0.45 mm) having a
thickness of 1.5 mm was prepared as the three-dimensional network
resin (one embodiment of the porous base composed of a resin
material). Then 90 g of graphite having an average particle
diameter of 0.5 .mu.m was dispersed in 0.5 L of a 10 mass % acrylic
acid ester-based resin aqueous solution to prepare a conductive
coating solution at this ratio.
The polyurethane foam sheet was continuously immersed in the
coating solution, squeezed by rollers, and dried to conduct an
electrical conduction treatment and form a conductive coating layer
on the surface of the three-dimensional network resin. The
viscosity of the conductive coating solution was adjusted with a
thickening agent. The coating solution was prepared in such a way
as to yield the desired alloy composition and adjust the coating
weight of the dried conductive coating solution to 69
g/m.sup.2.
A coating film of the conductive coating solution containing carbon
particles is formed on the surface of the three-dimensional network
resin through this step.
(Metal Plating Step)
The three-dimensional network resin subjected to the electrical
conduction treatment was electroplated to deposit 300 g/m.sup.2 of
nickel and then 75 g/m.sup.2 of a tin-chromium particle mixture by
using a tin plating solution containing dispersed chromium
particles having a volume-average particle diameter of 5 .mu.m so
as to form electroplating layers (an embodiment of the nickel layer
and the chromium-particle-containing tin layer). A nickel sulfamate
plating solution was used as the plating solution for nickel and an
organic acid bath was used as the plating solution for tin.
A nickel plating layer and a chromium-particle-containing tin
plating layer are formed on the coating film of the carbon
particle-containing conductive coating solution through this
step.
(Heat Treatment Step)
The porous metal body obtained through the steps described above
was first heat-treated in air at 800.degree. C. for 15 minutes so
as to burn away the three-dimensional network resin and the binder.
Then a heat treatment was conducted in a hydrogen atmosphere at
1000.degree. C. for 50 minutes so as to reduce the metals oxidized
by the in-air heat treatment and conduct alloying through thermal
diffusion.
The three-dimensional network resin is removed by pyrolysis through
this step. The nickel plating layer, the tin plating layer, and the
chromium particles contained in the tin plating layer are reduced
by the carbon particles contained in the conductive coating layer.
The nickel plating layer, the tin plating layer, and the chromium
component contained in the tin plating layer are alloyed through
thermal diffusion. Eventually, an porous alloy body (sample 1)
having a thickness of 1.5 mm, a metal plating weight of 375
g/m.sup.2, a nickel content of 80% by mass, a tin content of 15% by
mass, and a chromium content of 5% by mass was obtained.
(Example 2) Nickel Plating/Tin Plating/Chromium Sputtering
In Example 2, the process up to and including the electrical
conduction treatment was the same as that in Example 1 and the
detailed description therefor is omitted.
The three-dimensional network resin subjected to the electrical
conduction treatment was electroplated to deposit 300 g/m.sup.2 of
nickel and then 60 g/m.sup.2 of tin in a tin plating solution so as
to form electroplating layers (an embodiment of the nickel layer
and the tin layer). A nickel sulfamate plating solution was used as
the plating solution for nickel and a sulfuric acid bath was used
as the plating solution for tin.
A nickel plating layer and a tin plating layer are formed on the
coating film of the carbon-particle-containing conductive coating
solution through this step.
Next, 3 g/m.sup.2 of chromium was deposited onto the nickel-tin
porous body by sputtering. Sputtering was conducted in a sputtering
machine charged with an inert atmosphere gas and the gas pressure
during film deposition was 0.5 Pa.
Since the heat treatment step of Example 2 is identical to the heat
treatment step of Example 1, the detailed description therefor is
omitted.
The three-dimensional network resin is removed by pyrolysis through
the heat treatment step. The nickel plating layer, the tin plating
layer, and the sputtered chromium layer are reduced by carbon
particles contained in the conductive coating layer. The nickel
plating layer, the tin plating layer, and the sputtered chromium
layer are alloyed through thermal diffusion. Eventually, an porous
alloy body (sample 2) having a thickness of 1.5 mm, a metal plating
weight of 363 g/m.sup.2, a nickel content of 82.7% by mass, a tin
content of 16.5% by mass, and a chromium content of 0.8% by mass
was obtained.
(Example 3) Nickel Plating/Tin Plating/Chromium Plating
In Example 3, the process up to and including tin plating was the
same as that in Example 2 and the detailed description therefor is
omitted. A porous metal body with 300 g/m.sup.2 nickel and 60
g/m.sup.2 tin was obtained through the process so far.
Chromium plating was conducted by using a commercially available
trivalent chromium plating solution so that the chromium metal
plating weight was 30 g/m.sup.2.
The heat treatment step in Example 3 was identical to the heat
treatment step in Example 1 and the detailed description therefor
is omitted.
The three-dimensional network resin is removed by pyrolysis through
the heat treatment step. The nickel plating layer, the tin plating
layer, and the chromium plating layer are reduced by carbon
particles contained in the conductive coating layer. The nickel
plating layer, the tin plating layer, and the chromium plating
layer are alloyed through thermal diffusion. Eventually, an porous
alloy body (sample 3) having a thickness of 1.5 mm, a metal plating
weight of 390 g/m.sup.2, a nickel content of 76.9% by mass, a tin
content of 15.4% by mass, and a chromium content of 7.7% by mass
was obtained.
(Example 4) Nickel Plating/Tin Plating/Chromium Particle
Coating
In Example 4, the process up to and including tin plating was the
same as that in Example 2 and the detailed description therefor is
omitted. A porous metal body with 300 g/m.sup.2 nickel and 60
g/m.sup.2 tin was obtained through the process so far.
Subsequently, 12 g of chromium particles having a volume-average
particle diameter of 3 .mu.m were dispersed in 0.5 L of a 10 mass %
acrylic acid ester-based resin aqueous solution and a chromium
particle coating solution was prepared at this ratio.
Then the porous metal body was continuously immersed in the coating
solution, the excess coating solution was removed with an air
brush, and the porous metal body was dried so as to form a chromium
particle coating layer on the surface of the porous metal body. The
viscosity of the coating solution was adjusted with a thickening
agent. The coating solution was prepared so as to yield the desired
alloy composition and adjust the coating weight of the dried
conductive coating solution to 69 g/m.sup.2.
The heat treatment step in Example 4 was identical to the heat
treatment step in Example 1 and the detailed description therefor
is omitted.
The three-dimensional network resin is removed by pyrolysis through
this step. The nickel plating layer, the tin plating layer, and the
chromium particle coating layer are reduced by carbon particles
contained in the conductive coating layer. The nickel plating
layer, the tin plating layer, and the chromium particle coating
layer are alloyed through thermal diffusion. Eventually, an porous
alloy body (sample 4) having a thickness of 1.5 mm, a metal plating
weight of 373 g/m.sup.2, a nickel content of 80.3% by mass, a tin
content of 16.1% by mass, and a chromium content of 3.6% by mass
was obtained.
(Example 5) Nickel-Tin Alloy Plating/Chromium Sputtering
In Example 5, the process up to and including the electrical
conduction treatment was the same as that in Example 1 and the
detailed description therefor is omitted.
A commercially available plating solution was used for the
nickel-tin alloy plating, and a nickel-tin porous alloy body with a
metal plating weight of 360 g/m.sup.2 was obtained.
Chromium sputtering and a heat treatment were conducted as in
Example 2. Eventually, an porous alloy body (sample 5) having a
thickness of 1.5 mm, a metal plating weight of 363 g/m.sup.2, a
nickel content of 30.3% by mass, a tin content of 68.9% by mass,
and a chromium content of 0.8% by mass was obtained.
(Example 6) Nickel-Tin Alloy Plating/Chromium Plating
A nickel-tin porous alloy body was obtained as in Example 5, and
chromium plating and a heat treatment were conducted as in Example
3. Eventually, an porous alloy body (sample 6) having a thickness
of 1.5 mm, a metal plating weight of 390 g/m.sup.2, a nickel
content of 28.2% by mass, a tin content of 64.1% by mass, and a
chromium content of 7.7% by mass was obtained.
(Example 7) Nickel-Tin Alloy Plating/Chromium Particle Coating
A nickel-tin porous alloy body was obtained as in Example 5, and
chromium particle coating and a heat treatment were conducted as in
Example 4. Eventually, an porous alloy body (sample 7) having a
thickness of 1.5 mm, a metal plating weight of 373 g/m.sup.2, a
nickel content of 29.5% by mass, a tin content of 66.9% by mass,
and a chromium content of 3.6% by mass was obtained.
Comparative Example 1
In the description below, a nickel-tin porous alloy body of
Comparative Example 1 is described in detail.
(Electrical Conduction Treatment on Three-Dimensional Network
Resin)
A polyurethane foam sheet (cell size: 0.45 mm) having a thickness
of 1.5 mm was prepared as the three-dimensional network resin. Then
90 g of graphite having a volume-average particle diameter of 0.5
.mu.m was dispersed in 0.5 L of a 10 mass % acrylic acid
ester-based resin aqueous solution to prepare a conductive coating
solution at this ratio.
The polyurethane foam sheet was continuously immersed in the
coating solution, squeezed by rollers, and dried to conduct an
electrical conduction treatment and form a conductive coating layer
on the surface of the three-dimensional network resin. The
viscosity of the conductive coating solution was adjusted with a
thickening agent. The coating solution was prepared so as to yield
the desired alloy composition and adjust the coating weight of the
dried conductive coating solution to 55 g/m.sup.2.
A coating film of the carbon-particle-containing conductive coating
solution is formed on the surface of the three-dimensional network
resin through this step.
(Metal Plating Step)
The three-dimensional network resin subjected to the electrical
conduction treatment was electroplated to deposit 300 g/m.sup.2 of
nickel and then 53 g/m.sup.2 of tin so as to form electroplating
layers. A nickel sulfamate plating solution was used as the plating
solution for nickel and a sulfuric acid bath was used as the
plating solution for tin.
A nickel plating layer and a tin plating layer are formed on the
coating film of the carbon-particle-containing conductive coating
solution through this step.
(Heat Treatment Step)
The porous metal body obtained in the above-described step was
heat-treated in air at 800.degree. C. for 15 minutes to burn away
the three-dimensional network resin and the binder. Subsequently, a
heat treatment at 1000.degree. C. was conducted for 50 minutes in a
hydrogen atmosphere to reduce the metals oxidized in the in-air
heat treatment and conduct alloying through thermal diffusion.
The three-dimensional network resin is removed by pyrolysis through
this step. The nickel plating layer and the tin plating layer are
reduced by carbon particles contained in the conductive coating
layer and alloyed through thermal diffusion. Eventually, an porous
alloy body (sample 11) having a thickness of 1.5 mm, a metal
plating weight of 353 g/m.sup.2, a nickel content of 85% by mass,
and a tin content of 15% by mass was obtained.
Comparative Example 2
In the description below, a nickel-chromium porous alloy body of
Comparative Example 2 is described in detail.
(Electrical Conduction Treatment on Three-Dimensional Network
Resin)
First, a polyurethane foam sheet (cell size: 0.45 mm) having a
thickness of 1.5 mm was prepared as the three-dimensional network
resin. Then 90 g of graphite having a volume-average particle
diameter of 0.5 .mu.m was dispersed in 0.5 L of a 10 mass % acrylic
acid ester-based resin aqueous solution to prepare a conductive
coating solution at this ratio.
The polyurethane foam sheet was continuously immersed in the
coating solution, squeezed by rollers, and dried to conduct an
electrical conduction treatment and form a conductive coating layer
on the surface of the three-dimensional network resin. The
viscosity of the conductive coating solution was adjusted with a
thickening agent. The coating solution was prepared so as to yield
the desired alloy composition and adjust the coating weight of the
dried conductive coating solution to 55 g/m.sup.2.
A coating film of the conductive coating solution containing carbon
particles is formed on the surface of the three-dimensional network
resin through this step.
(Metal Plating Step)
The three-dimensional network resin subjected to the electrical
conduction treatment was electroplated to deposit 300 g/m.sup.2 of
nickel so as to form an electroplating layer. A nickel sulfamate
plating solution was used as the plating solution for nickel.
A nickel plating layer is formed on the coating film of the
carbon-particle-containing conductive coating solution through this
step.
(Heat Treatment Step)
The porous metal body obtained in the above-described step was
heat-treated in air at 800.degree. C. for 15 minutes to burn away
the three-dimensional network resin and the binder. Subsequently, a
heat treatment at 1000.degree. C. was conducted for 50 minutes in a
hydrogen atmosphere to reduce the metals oxidized in the in-air
heat treatment.
The three-dimensional network resin is removed by pyrolysis through
this step. The nickel plating layer is reduced by carbon particles
contained in the conductive coating layer.
(Chromium Diffusing Step)
The nickel porous body obtained in the above-described step was
subjected to a chromizing treatment (powder-pack method) to diffuse
chromium. The nickel porous body was charged with a penetrant
(chromium: 90% by mass, NH.sub.4Cl: 1% by mass, Al.sub.2O.sub.3: 9%
by mass) obtained by mixing chromium particles, ammonium chloride,
and alumina particles, and heated to 800.degree. C. in a hydrogen
gas atmosphere to obtain a nickel-chromium porous alloy body.
Eventually, an porous alloy body (sample 12) having a thickness of
1.5 mm, a metal plating weight of 460 g/m.sup.2, a nickel content
of 65% by mass, and a chromium content of 35% by mass was obtained
by adjusting the heating time in the chromizing treatment.
(Measurement of Surface Chromium Concentration)
The front side and the back side of each of the sheet samples
(samples 1 to 7, 11, and 12) obtained in Examples and Comparative
Examples above were analyzed with X-ray fluorescence to determine
the surface chromium concentration of the skeleton. The measurement
results are shown in Table 1 below. A portable-type X-ray
fluorescence analyzer (NITON XL3t-700 produced by Thermo Fisher
Scientific) was used in the measurement. Measurement was conducted
by bringing the measuring unit into contact with the surface of the
porous metal body to be measured.
TABLE-US-00001 TABLE 1 Compositional ratio calculated Surface
chromium from metal content (mass %) concentration (mass %) Sample
Nickel Tin Chromium Front side Back side Sample 1 80.0 15.0 5.0
34.1 33.1 Sample 2 82.6 16.5 0.8 25.6 27.2 Sample 3 76.9 15.4 7.7
37.5 36.4 Sample 4 80.3 16.1 3.6 32.5 32.7 Sample 5 30.3 68.9 0.8
24.3 23.2 Sample 6 28.2 64.1 7.7 35.9 33.8 Sample 7 29.5 67.0 3.6
30.4 31.5 Sample 11 85.0 15.0 -- -- -- Sample 12 65.0 -- 35.0 34.7
36.2
Table 1 shows that the metal porous bodies of samples 1 to 7 have
high surface chromium concentrations compared to the chromium
compositional ratios calculated from the metal contents (average of
the chromium compositional ratio when the sample is viewed as a
whole).
Specifically, the surface chromium concentration of each of the
metal porous bodies of samples 1 to 7 is about 4 to 30 times higher
than the chromium compositional ratio calculated from the metal
content.
Accordingly, the concentration of chromium contained in the metal
porous bodies of samples 1 to 7 is highest at the surface of the
skeleton of the porous metal body and decreases toward the inner
side of the skeleton.
In contrast, in the porous metal body of sample 12, the surface
chromium concentration is about the same as the chromium
compositional ratio calculated from the metal content.
Accordingly, the concentration of chromium contained in the porous
metal body of sample 12 at the surface of the skeleton is nearly
the same as that of the inner side of the skeleton.
(Corrosion Resistance Test)
A test based on ASTM G5-94 was performed to evaluate corrosion
resistance of the sheet samples (samples 1 to 7, 11, and 12)
obtained in Examples and Comparative Examples described above. The
aqueous acidic solution used for anodic polarization curve
measurement was prepared by adjusting pH of a 1 mol/L aqueous
sodium sulfate solution with sulfuric acid.
The test temperature was 60.degree. C. During testing, a hydrogen
saturation state was created by hydrogen bubbling. The potential
range for voltammetry was 0 V to 1.0 V relative to the standard
hydrogen electrode since this range was considered to be the range
that might actually be applied in the fuel cell, and the sweeping
rate was 5 mV/s.
Regarding the corrosion resistance test, evaluation can be made on
the basis of the value of the anodic current in the potential range
actually used in the fuel cell through performing anodic
polarization measurement on the material. The anodic polarization
curve measurement of metal materials is described in JIS G 0579
(JIS G 0579, "Method of anodic polarization curves measurement for
stainless steels") and ASTM G5-94 (ASTM G5-94 (2004), Standard
Reference Test Method for Making Potentiostatic and Potentiodynamic
Anodic Polarization Measurements). In particular, ASTM G5-94
describes evaluation of fuel cells and is employed in corrosion
resistance test for materials in the field of fuel cells; thus,
evaluation was made based on this technique (Chih-Yeh Chung, et
al., J. Power Sources, 176, pp. 276-281 (2008), Shuo-Jen Lee, et
al., J. Power Sources, Volume 131, Issues 1-2, pp. 162-168 (2004),
M. Rendon-Belmonte ("o" in Rendon is with an acute accent), et al.,
Int. J. Electrochem. Sci., 7, pp. 1079-1092 (2012)).
(Results of Corrosion Resistance Test)
The current values at ASTM test potentials of 0.2 V and 0.8 V were
measured from the sheet samples (samples 1 to 7, 11, and 12)
obtained in Examples and Comparative Examples described above. The
test was performed five times. The observed current values at the
first cycle and the fifth cycle are shown in Table 2.
TABLE-US-00002 TABLE 2 Current value Current value at first cycle
at fifth cycle Sample of ASTM (mA) of ASTM (mA) Test potential 0.2
V 0.8 V 0.2 V 0.8 V Sample 1 1.18 0.77 1.16 0.75 Sample 2 1.25 0.89
1.27 0.87 Sample 3 0.99 0.63 1.01 0.62 Sample 4 1.2 0.79 1.17 0.78
Sample 5 1.28 0.93 1.26 0.94 Sample 6 1.11 0.72 1.12 0.74 Sample 7
1.21 0.82 1.23 0.79 Sample 11 1.65 2.53 2.28 2.61 Sample 12 0.16
5.9 0.96 7.7
Table 2 shows that the current values of samples 1 to 7 are lower
than the current value of the sample 11 at both test potentials,
0.2 V and 0.8 V.
This shows that samples 1 to 7 have higher corrosion resistance
than sample 11.
Samples 1 and 2 are compared with sample 12. At a test potential of
0.2 V, the current values of samples 1 and 2 are larger than that
of sample 12. However, at a test potential of 0.8 V, the current
values of samples 1 and 2 are about 1/5 of that of sample 12.
This shows that samples 1 and 2 have higher high-voltage-side
corrosion resistance than sample 12.
The current values of samples 1 to 7 after the corrosion resistance
test was repeated (current values at the fifth cycle) do not change
significantly whereas the current value of sample 11 shows an
increase at 0.2 V and the current value of sample 12 shows an
increase at both 0.2 V and 0.8 V.
This shows that samples 11 and 12 have corrosion resistance
degraded after repeating the corrosion resistance test.
The results described above show that samples 1 to 7 have superior
durability to samples 11 and 12.
The embodiments disclosed herein are merely exemplary in all
aspects and should not be construed as limiting. The scope of the
present invention is defined not by the description above but by
the claims and is intended to include all modifications within the
meaning and the scope of the claims and equivalents thereof.
* * * * *